Just some quick noob questions...
What causes low vacuum readings?
Would bad compression also cause vacuum to drop with it?
Would vacuum leaks cause low vacuum?
What vacuum should stock ports be on?

Joseph

 

What causes low vacuum readings?

You probably have a vacuum leak either a hose has popped off or you may have a cracked hose. If not, it could be a number of things such as faulty actuators, cracked vacuum chamber, etc.


Would bad compression also cause vacuum to drop with it?
IF you are talking about low rotor compression then my first question is how low? Below 85psi on all three sides? Is so, you need a new engine then trouble shoot vacuum leak. Now having said that, a low vacuum reading will not affect your rotor/engine compression.


Would vacuum leaks cause low vacuum?
YES


What vacuum should stock ports be on?
If you are talking about ports that you connect your vacuum hoses to then there are LOTS... you need to search under 3rd gen FAQ for a vacuum diagram. It's pretty complex but knowledge and understanding is a must if you own an FD.

J

 

Those are the two main reasons for low vacuum. However, RPM is a third major factor. The faster the engine rotors are spinning, the higher the effective manifold vacuum. It's also why compression tests must have the cranking RPM measured with it. So if your idle rpm is low, the idle vacuum will probably decrease a little too.

Compression also changes a little depending on if the engine is cold (higher comp. readings) or hot (lower compression readings). Like RPM, the engine temp can affect compression and vacuum by several percent.

I think 15-20inHg, for a new motor with stock porting and throttle body, and excellent compression.

Dave

 

Thanks alot guys, appreciate it.